In the petroleum industry it is a well known practice in the completion of new wells and the workover of existing wells to employ explosives to stimulate the flow of oil and/or gas from hydrocarbon bearing formations. Various types of explosive formulations have been used in such procedures. Historically, explosives used in well stimulation have taken the form of high energy explosives of high detonation velocities. Uren, L. C. "Petroleum Production Engineering-Oil Field Development," 3rd Edition, 1952 McGraw Hill, under the heading "Use of Explosives in Well Completion", pages 588-593, discloses use of explosives such as dynamite, nitroglycol or nitroglycerin having detonation velocities in excess of 20,000 feet per second. The use of such explosives is also disclosed in the companion volume by Uren, "Petroleum Production Engineering-Oil Field Exploitation", 3rd Edition, 1953, at pages 165 and 419-424. Emphasis is placed not only on fracturing the surrounding subterranean formation, but also on forming cavities in the well to enlarge the effective diameter of the well at the formation face.
A somewhat different approach in explosive well stimulation involves the use of explosives of relatively low detonation velocity as disclosed in U.S. Pat. No. 4,490,196 to Funk. The compositions in Funk are formulated from a first explosive component mixture, specifically, a 40-60/60-40 mixture of metriol trinitrate and diethylene glycol dinitrate; a second component (termed an ester component although not all of the second component compounds are esters) taking the form of an aromatic diester, a trialkylaryl phosphate such as tricresyl phosphate, or a mono or polyacetyl alkane; and an organic stabilizer component such as ethyl centralite. The explosive formulations disclosed in Funk are said to have slow detonation velocities within the range of about 1200-2500 meters/second. The low detonation velocity explosive formulations exhibit a small shockwave component in relation to the total explosive energy and provide a maximum pressure less than the yield stress of the rock formation surrounding the wellbore in which the charge is detonated. This minimizes formation of a residual stress field due to plastic deformation of the rock and minimizes direct borehole damage at the rock face. U.S. Pat. No. 4,555,279 to Funk is a continuation in part of Funk '196 and discloses an alkylaryl dinitrate as an alternative to the ester components of Funk '196. The explosive component may be metriol trinitrate, diethylene glycol dinitrate, or nitroglycerine.
Whereas the patents to Funk disclose the use of diesters of polybasic aromatic acids to arrive at explosive formulations of reduced detonation velocity, U.S. Pat. No. 4,595,430 to Baker discloses the use of diesters in which the acid component does not contain a benzyl group to desensitize a dynamite composition to impact detonation while only minimally reducing explosive characteristics such as velocity or rate of detonation velocity buildup. The diester desensitizer of U.S. Pat. No. 4,595,430 is employed in the dynamite in relative small amounts; in a range of 0.5-5.0 wt. % preferably 1.5 to 2.5 wt. %. The desensitizers disclosed there include diesters of dibasic acids having from 5 to 12 carbon atoms, including diesters of glutaric, adipic, and sebacic acids. Triesters or polyesters, exclusive of those containing benzene rings can also be employed as desensitizers. Preferred desensitizers include triethylene glycol caprate caprylate, mixed diesters produced by reacting isodecyl and 2-ethyl hexanol with a mixture of C.sub.4 -C.sub.9 dicarboxyalic acids and triethylene glycol dipelargonate, glyceryl triacetate or glyceryl triproprionate.
U.S. Pat. No. 3,116,188 to Austin discloses the use of surface active agents to desensitize liquid explosives such as ethylene glycol dinitrate and nitroglycerine to impact detonation. Included as desensitizers are polyesters of polybasic aliphatic acids in which the esterifying portion contains from 3 to 7 carbon atoms. Specifically disclosed are tributyrin, tricaproin, and di-n-butyl sebacate used in amounts of 10-30%.
U.S. Pat. No. 4,292,098 to Mastroianni et al discloses liquid gun propellants based upon liquid nitrate esters or nitroparaffins containing a diluent or desensitizing agent in the form of a diester of C.sub.7 -C.sub.9 dicarboxylic acids and C.sub.3 -C.sub.5 alcohols. The preferred esters are azelates with isopropyl or isobutyl ester groups. The desensitizing ester is present in an amount within the range of 5-25 wt. %. A stabilizer such as 2-nitrodiphenylamine, resorcinol or ethyl centralite may also be employed in an amount of 1-4%.